In recent years, from the viewpoint of energy conservation and miniaturization, illumination apparatuses using light emitting diodes (hereinafter also referred to as “LED”) as light sources, (LED flashes), have been used as light emitting devices for imaging cameras. As the light emitting devices described above, light emitting devices in which an LED and a Fresnel lens are combined are well known.
Generally, as a means for combining an LED and a Fresnel lens, a method has been employed in which using an adhesive a Fresnel lens is fixed to a substrate on which an LED is mounted. At that time, the Fresnel lens is fixed to the substrate via supporting parts joined to the substrate. When the Fresnel lens is thus fixed using an adhesive, there is a risk that the adhesive undesirably sticks to an optical surface of the Fresnel lens and reduces the optical performance of the light emitting device. As a means for solving such a drawback, a Fresnel lens has been proposed that is provided with an adhesion target part at the outside of the optical surface (see, e.g., PTL 1).
FIGS. 1A, 1B and 1C are schematic diagrams illustrating a configuration of Fresnel lens 10 disclosed in PTL 1. FIG. 1A is a side view of Fresnel lens 10, FIGS. 1B and 1C are side views illustrating a mode in which Fresnel lens 10 is adhered to supports 20. As illustrated in FIG. 1A, Fresnel lens 10 has substrate 12 for supporting Fresnel lens 10, lens part 14 disposed on substrate 12, and protrusion parts 16 disposed outside lens part 14 on substrate 12. As illustrated in FIG. 1B, when Fresnel lens 10 is adhered to supports 20, adhesive 30 is first applied to support attaching surfaces 18 positioned outside protrusion parts 16 on substrate 12. Next, as illustrated in FIG. 1C, adhesive 30 is cured while the end surfaces of supports 20 are pressed against support attaching surfaces 18, thereby enabling Fresnel lens 10 to be adhered to supports 20. At that time, protrusion parts 16 prevent adhesive 30 from being pressed and spread to reach lens part 14. Thus, it is possible to prevent a decrease in the optical performance due to sticking of adhesive 30.